1. Field of the Invention
The present invention relates to a series of step-up or reduction gears using an internally meshing planetary gear structure.
2. Description of the Prior Art
Conventionally, there has been known a multi-line type internally meshing planetary gear structure. It includes a first shaft; eccentric bodies rotated by the rotation of the first shaft; a plurality of external gears mounted on the eccentric bodies through bearings to be freely eccentrically rotated around the first shaft; and an internal gear internally meshing with the external gears through internal teeth constituted of external pins; and a second shaft connected to the external gears through inner rollers for taking out only rotational component of the external gears.
A conventional example of such a structure is shown in FIGS. 3 and 4. In this example, the above first shaft corresponds an input shaft and the second shaft corresponds an output shaft, and further, the internal gear is fixed. Thus, this structure is applied to a reduction gear.
Eccentric bodies 3a and 3b are fitted around an input shaft 1 with a specified phase difference respectively (180.degree. in this example). The eccentric bodies 3a and 3b are disposed to be eccentric with the input shaft (center O.sub.1) by an eccentric amount e (center O.sub.2), respectively. Two external gears 5a and 5b are mounted in a multi-line around the eccentric bodies 3a and 3b through bearings 4a and 4b, respectively. A plurality of inner roller holes 6a and 6b are provided on the external gears 5a and 5b, respectively. Inner pins 7 and inner rollers 8 are inserted in the inner roller holes 6a and 6b, respectively.
To increase the transmission capacity, hold the strength and keep the rotational balance, the external gears are disposed in a multi-line.
The external teeth 9 having a trochoidal teeth shape, a circular-arc teeth shape or the like are provided around the outer periphery of each of the external gears 5a and 5b. The external teeth 9 internally mesh with the internal gear 10 fixed on a casing 12. The internal teeth of the internal gear 10 have such a structure that the external pins 11 are freely inserted and held in external pin holes 13 in a manner to be easily rotated, respectively. The internal pins 7 passing through the external gears 5a and 5b are rigidly fixed or fitted in the casing 12 near an output shaft 2.
With the input shaft 1 rotated by one time, the eccentric bodies 3a and 3b are also rotated by one time. By the one rotation of the eccentric bodies 3a and 3b, the external gears 5a and 5b are intended to be rotated around the input shaft 1. However, since the internal gear 10 is restricted in its rotation, the external gears 5a and 5b are almost swayed while internally meshing with the internal gear 10.
Assuming that the number of the gear teeth in the external gears 5a and 5b is taken as N, and the number of the gear teeth in the internal gear 10 is taken as (N+1), the difference in the number of the gear teeth becomes 1. Accordingly, the external gears 5a and 5b are shifted (rotated) by one gear tooth with respect to the internal gear 10 fixed on the casing 2 for each rotation of the input shaft 1. Namely, one rotation of the input shaft 1 is reduced in the rotation of -1/N of the external gears 5a and 5b.
As for the rotation of the external gears 5a and 5b, the swaying component is absorbed by gaps between the inner roller holes 6a and 6b and the inner pins 7 (inner rollers 8), and thus only the rotational component is transmitted to the output shaft 2 through the inner pins 7. This makes it possible to achieve the reduction at a reduction ratio of -1/N.
The internally meshing planetary gear structure described above has been applied to various types of reduction gears or step-up gears. In the above structure, the first shaft corresponds an input shaft and the second shaft corresponds an output shaft, and further, the internal gear is fixed. However, for example, if the first shaft corresponds an input shaft and the internal gear corresponds an output shaft, and further, the second shaft is fixed, then, that can also constitute a reduction gear. Further, in these structures, it is possible to constitute a step-up gear by replacing the input shaft by the output shaft.
FIG. 5 shows an example wherein the above structure is of a unit type (Japanese Patent Laid-open No. sho 62-2043). In this structure, an output shaft 2 is mounted on the mating-machine through a bolt hole 14, wherein the internally meshing planetary gear structure itself is the same as shown in FIGS. 3 and 4. Accordingly, the members corresponding to those as shown in FIGS. 3 and 4 are designated at like reference characters. The internally meshing planetary gear structure is also used in the reduction gear or step-up gear of this type.
In the gear transmission mechanism, a gap or looseness is generally present between gears meshing with each other or in the mounting means to the shaft. As a consequence, when the normal rotation is converted to the reverse rotation, the reverse on the drive side does not appear instantly as the reverse on the driven side.
Hereinafter, for convenience, the gap or looseness generated in conversion from the normal rotation to the reverse rotation is referred to as "angular backlash". Namely, the angular backlash means how the input shaft should be reversed in order to reverse the output shaft accompanied therewith. In other words, the angular backlash is defined as an amount (angle) which permits the other shaft to move in the state that one shaft (low speed side or high speed side) is stopped. Therefore, the angular backlash does not mean how the gap is present in the state that each gear or the like is assembled.
In the transmission mechanism using a multi-line type internally meshing planetary gear structure described above, generally, the gaps or loosenesses at respective meshed portions interfere with each other so that such an angular backlash is made to be relatively smaller.
However, even in the above gear structure, since the driving power is transmitted by the meshing between gears, the angular backlash, while being small, is generated in conversion from the normal rotation to the reverse rotation as a necessity. When the transmission mechanism is used as a controller dealing with the normal and reverse rotations, the presence of such an angular backlash unfavorably lowers the accuracy. Also, it has a tendency of generating a shock, which is inconvenient in terms of the mechanical durability of the transmission mechanism itself.
For making smaller the above angular backlash, there has been adopted a technique of enhancing the machining accuracies of the parts, or of selectively assembling the parts to be used.
Also, in Japanese Patent Laid-open No. sho 59-106744 (Japanese Patent Publication No. hei 3-3820) or the like, an eccentric body is axially divided in correspondence with external gears, and mounting means for mounting the divided eccentric bodies to a shaft are rotatable with respect to the shaft. Thus, by giving the "pre-loading" on the divided eccentric bodies in the reverse directions, in the mounted state, the angular backlash in the normal rotation is removed by one divided eccentric body, whereas the angular backlash in the reverse direction is removed by the other divided eccentric body.
In Japanese Utility Model No. sho 56-35552, an internal gear 10 and outer pins 11 are axially divided in correspondence with external gears 5a and 5b, and mounting means for mounting the divided internal gears 10 to a casing 12 are rotatable with respect to the casing 12. Thus, by giving the "pre-loading" on the divided internal gears 10 in the reverse directions, in the mounted state, the angular backlash in the normal rotation is removed by one divided internal gear, whereas the angular backlash in the reverse direction is removed by the other divided internal gear.
Incidentally, in the internally meshing planetary gear structure described above, the reduction gear ratio can be freely changed only by changing the external gears 5a and 5b, internal gear 10, external pins 11 and eccentric bodies 3a and 3b.
Thus, it is possible to cope with the various requirements of users by previously preparing a sub-series (hereinafter, referred to as "frame number"). In the respective frame number, the mating dimensions (sizes) to the mating-machine determined by the dimensions (sizes) of the output shaft 2 and the casing 12 are determined in several kinds according to the market requirement. And in time same frame number, the several kinds of the speed change ratios are previously set.
Concretely, in a well-known example, there have been prepared the reduction gears, in various frame numbers, which have reduction gear ratios of from 1/6 to 1/119, motor assemblies of from 0.1 kw to 132 kw, and output torques of from 0.35 kgm to 6000 kgm.
However, the conventional reduction gear series using the internally meshing planetary gear structure has not sufficiently coped with the diversification of motors and their usages accompanied with the rationalization in the recent production system.
For example, in the field of the physical distribution system frequently using the reduction gears of this kind, it is effective to operate the necessary parts of the physical distribution system constituted of a plurality of conveyors at the necessary timing. Consequently, the conveyors have been required to be independently driven.
Further, two kinds of conveyors have been required in terms of the function. One is enough to have the function of only moving matters to be carried. The other requires the carrying speed control and the stopping control at the specified position. Hereinafter, for convenience, the former is referred to as "general conveyor", and the latter is referred to as "control conveyor".
In general, the general conveyor uses the assembly of the cage type induction motor and the reduction gear. On the other hand, the control conveyor uses the assembly of the servo-motor and the reduction gear. As the reduction gear assembled with the servo-motor, there has been required a low backlash type reduction gear, which has a small angular backlash and is suitable for the stopping control at the specified position.
In the viewpoint of the reduction gear used in such a conveyor, since the reduction gear only constitutes a part of the mating-machine (conveyor or the like), and further, since the mating-machine only constitutes a part of the whole physical distribution system, accordingly, there are cases that the reduction gear is required the function as the general conveyor, and occasionally is required the function as the control conveyor in the relationship with the whole physical distribution system.
On the other hand, for improvement in the maintenance performance or the productivity of the whole system, it is convenient to reduce the kinds of the conveyors in one system. Namely, it is desirable to suitably change the general conveyor into the control conveyor only by changing the reduction gear and the motor (and its controller).
However, the prior arts and commercial reduction gear series could not meet the above requirements.
Namely, in the so-called "pre-loading" disclosed in Japanese Patent Laid-open No. sho 59-106744 and Japanese Utility Model No. sho 56-35552, the plural external gears are provided in the multi-line for increasing the transmission capacity and holding the strength. However, actually, in the normal rotation, the power si transmitted only by the external gear without the angular backlash in the normal direction, whereas in the reverse rotation, the power is transmitted only by the external gear without the angular backlash in the reverse direction. Consequently, there has arisen a new problem of making wasteful the advantage obtained by the multi-line mechanism described above.
In other words, in the "pre-loading" in Japanese Patent Laid-open No. sho 59-106744 and Japanese Utility Model No. sho 56-35552, although the angular backlash is reduced, the transmission torque capacity is reduced by half. Accordingly, in order to obtain the same transmission torque capacity, the reduction gear in a larger frame number (the mounting dimension (size) is made larger) is required. This causes such a disadvantage of eliminating the interchangeability. Further, according to the space environment, a problem is encounted in that the reduction gear as the control conveyor cannot be mounted on such a location that the reduction gear as the general conveyor can be mounted.